The invention relates to a Kellybar drilling device which is particularly suitable for pile drillings.
For making foundation bores for piles, Kellybars are used which are telescopable to reach drilling depths greater than the drilling mast length without the use of extension segments. The Kellybar consists of an outer tube and at least one telescopic tube arranged therein and being displaceable thereout, which is lockable to the outer tube to transfer the torque required for drilling and the axial thrust forces to the drilling tool. The drilling tools which are typically used and mounted to the front end of the innermost telescope tube are rotary drilling tools (augers, drill buckets, core drilling auger bits) which receive the earth in the drill hole. When the rotary drilling tool is filled with earth, the Kelly system is drawn up with a rope, the tubes of the Kellybar telescoping into each other.
Primarily, the conventional Kellybar systems with rotary drilling tools can only be applied in non-rocky ground, but fail when there are pieces of rock or similar hindrances in the ground which cannot be overcome by dry rotary drilling. A pressure medium like compressed air or liquid cannot be fed to the tool through a Kellybar because the pressure medium would escape at the connection spots of the tubes of the Kellybar. For the same reason, it is not possible to perform flush drillings in which case a flushing agent is introduced into the drilling hole to flush out the drilling stock.